JP2921977B2 - Process and equipment - Google Patents

Abstract

Esterification is carried out in a column reactor (14) in which there is a plurality of esterification trays (15) each having predetermined liquid hold-up and containing a charge of a solid esterification catalyst thereon. e.g. an ion exchange resin containing a -SO3H and/or -COOH groups. A liquid phase containing the carboxylic acid component, e.g. a fatty acid mixture, flows down the column reactor from one esterification tray to the next downward one against an upflowing alcohol vapour stream, e.g. methanol vapour. Relatively dry alcohol vapour is injected (21) into the bottom of the column reactor. Water of esterification is removed from the top of the column reactor in the vapour stream (26), whilst ester product is recovered (23) from the sump of the reactor. As the liquid flows down the trays it encounters progressively drier alocohol and the esterification equilibrium reaction is driven further and further towards 100% ester formation. A polishing reactor (304) operated under liquid phase conditions may follow the column reactor, the ester-containing product from which is mixed with further alcohol before admission to the polishing reactor.

Description

The present invention relates to a process and an apparatus for the production of carboxylic esters.

Esterification is a well-known equilibrium limited reaction involving the reaction of mono-, di- or polycarboxylic acids (or anhydrides, where appropriate) with an alcohol or phenol component. Such alcohol or phenol components may be monovalent, divalent or polyvalent.

For example, in the production of a monoester, the reaction can be summarized as follows: Here, R ¹ is a hydrogen atom or a monovalent organic group, and R ² is a monovalent organic group. When an anhydride is used as the acid component, the reaction takes place in two stages: Here, R ³ is a divalent organic group, or R ⁴ is a monovalent organic group.

The reaction of formula (2) above will usually proceed in the absence of an added catalyst, and organic acids may autocatalyze reactions (1) and (3) to some extent, but accelerate the reaction. It is usual practice to add a catalyst to the esterification reaction mixture for this purpose.

Probably the most widely used catalysts are sulfuric acid and organic sulfonic acids such as p-toluenesulfonic acid. Although these catalysts are effective, they are homogeneous catalysts and a neutralization step is required before ester purification can be contemplated. Typically, washing with an alkali such as sodium hydroxide solution is used in such a neutralization step. The disadvantage of this process is that the esterification is an equilibrium process, and the washing step also results in the removal of unreacted carboxylic acid into the washing liquor. It is uneconomic to attempt to recover the unreacted acid from its salts in the wash liquor, and this may represent a significant loss in process efficiency. In addition, some esters may be lost in this washing step. The loss of the ester in the aqueous alkaline solution phase is determined by the solubility of the ester in such a solution. The sodium salt of the partially esterified polycarboxylic acid will also be soluble in aqueous alkaline solutions. The loss of such partially esterified polycarboxylic acids will in this case represent the loss of both the acid moieties and also the alcohol moieties. Furthermore, the treatment of the washing solution may cause environmental problems, which can be augmented by the presence of organic carboxylate in the washing solution. In addition, problems can arise due to the formation of emulsions in the washing step, especially when long chain fatty acids are involved. That is, the emulsions are stabilized by surface-active alkali metal fatty acid salts and are often difficult to separate into their component aqueous and organic phases. It is known that the stability of such emulsions varies in a whimsical manner, thus making it difficult to design organic / aqueous phase separation equipment. It is therefore difficult to carry out the esterification process on a continuous basis with homogeneous catalysts. As a result, batch processing is commonly employed, which can affect product quality from batch to batch. An additional disadvantage of such homogeneous catalysts is the risk of ester contamination by sulfur-containing components. Such sulfur-containing components can significantly interfere with subsequent chemical process steps.

As a result of recent work performed in our laboratory, a continuous process for the production of dialkyl maleates using acidic ion exchange resins as catalysts has been proposed. This proposal is described in EP-A-0255399 and WO-A-88 / 00937. According to this proposal, dialkyl maleate causes the liquid feed mixture containing the monoalkyl maleate to flow countercurrently to the stream of vaporous alkanol vapor, so that the liquid phase passes through one or more catalyst-containing esterification zones. In this case, it is produced by encountering a drier alcohol vapor. In another embodiment, a number of continuously stirred tank reactors are used, with the liquid phase passing from one reactor to the next, while alcohol vapor is passed from each reactor to the preceding row in the row. To the reactor.

The proposals described in EP-A-0255399 and WO-A-88 / 00937 are somewhat complicated. The tower concept requires that the ion exchange resin be packaged in individual mesh packages. Multi-reactor systems require continuous operation of the stirrer motor and are somewhat difficult to control in practice, in addition to requiring a substantial footprint for construction.

One form of gas-liquid contact column is described in US-A-3394927. DE-B-1009749 describes a column reactor for hydrogenating unsaturated oils. FR-A-1384683 describes a multi-compartment column reactor in which the catalytic reaction flows counter-currently from compartment to compartment and within each compartment between gas and liquid flowing co-currently. Can be accomplished.

The present invention is an improved continuous process for the production of esters using ion exchange resin catalysts, eliminating the need for simple and continuous mechanical stirring in operation,
On the other hand, there is a need to create a process that allows the use of free fine-grained ion exchange resin.

According to the present invention, mono-, di- and polycarboxylic acids,
For the production of carboxylic acid esters by reacting a carboxylic acid component selected from their anhydrides and mixtures thereof with an alcohol component selected from monohydric, dihydric and polyhydric alcohols, phenols and mixtures thereof Wherein the carboxylic acid component and the alcohol component are
Esterification in a process maintained under esterification conditions and passed countercurrently through an esterification zone containing a solid esterification catalyst selected from particulate ion exchange resins having sulfonic acid groups, carboxylic acid groups, or both. The zone has a column reactor with a plurality of esterification trays located one above the other, each tray holding a predetermined liquid volume and a certain amount of solid esterification catalyst thereon. Having liquid downcomer means associated with each of the esterification trays, allowing the liquid phase to pass down the column reactor from the esterification tray but retaining the solid esterification catalyst thereon; Vapor riser means in combination with the esterification tray, wherein steam enters the esterification tray from below, and a mixture of liquid and solid esterification catalyst on the tray With stirring, the less volatile component of the carboxylic acid component and the alcohol component is supplied in the liquid phase to the top tray of the plurality of esterification trays, while the carboxylic acid component and the alcohol component are The more volatile components of are supplied in vapor form under the bottom tray of the plurality of esterification trays, and the vapors of the more volatile components and the water of esterification are supplied from the top of the column reactor. A continuous process for the production of carboxylic esters is provided, wherein the carboxylic esters are recovered from the lower part of the column reactor.

The invention further comprises a carboxylic acid component selected from mono-, di- and polycarboxylic acids, their anhydrides and mixtures thereof, and mono-, di- and polyhydric alcohols, phenols and mixtures thereof. An apparatus used for the production of a carboxylic acid ester by reaction with an alcohol component, comprising a column reactor with a plurality of esterification trays arranged one above the other, each tray being defined in advance. A liquid downcomer means associated with each of the esterification trays and adapted to hold a liquid amount and a certain amount of a solid esterification catalyst thereon; Through which the solid esterification catalyst is retained, and has steam riser means in combination with each esterification tray so that the steam is Into the mixture from below, and the mixture of the liquid and the solid esterification catalyst on the tray is agitated. Means for feeding to the top of the column reactor above the top tray in the esterification tray and the more volatile components of the carboxylic acid and alcohol components below the bottom esterification tray. A means for feeding in vapor form to the top of the column reactor; a means for recovering the carboxylic acid ester from below the column reactor below the lowermost esterification tray; Means for the production of carboxylic esters comprising means for recovering a vapor stream consisting of the more volatile components and the water of esterification above the top esterification tray. To.

The process of the present invention transports the vapor stream of the more volatile of the two components, the carboxylic acid component and the alcohol component, off of the esterified water formed in the esterification reactor. For this purpose, however, the other of the two components, namely the less volatile or a significant amount of the carboxylic acid ester, is utilized without carrying it with it. For this reason, the boiling point of the vapor mixture exiting the esterification reactor, or the boiling point of the highest boiling compound present in the vapor mixture, at the pressure governing the uppermost stage of the esterification reactor, the two components It is essential that any of the less volatile ones, i.e., the less volatile ones of the carboxylic acid component and the alcohol component, or the carboxylic ester product, be significantly lower than the boiling point at that pressure. By the term “significantly lower” we mean that the boiling point difference is at least about 20 ° C., and preferably at least about 25 ° C., at the operating pressure.

Examples of monoesterification reactions that can be performed according to the present invention may include the preparation of alkyl esters of aliphatic monocarboxylic acids from alkanols and aliphatic monocarboxylic acids or anhydrides. Such monocarboxylic acids can contain, for example, from about 6 to about 26 carbon atoms, and can include mixtures of two or more. Of particular interest are alkyl esters derived from alkanols containing from 1 to about 10 carbon atoms.

Such monocarboxylic acids include decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, octadecenoic acid, linolenic acid, eicosanoic acid, isostearic acid, and the like, as well as mixtures of two or more thereof. Mixtures of fatty acids are produced commercially by hydrolysis of naturally occurring triglycerides of plant origin, such as coconut oil, rapeseed oil and palm oil, and triglycerides of animal origin, such as lard, tallow and fish oil. If desired, the acid mixture is subjected to distillation, chosen to remove low boiling acids (e.g., acid C ₈ to C ₁₀₎ from having a boiling point lower than the temperature, cut the top of it with an acid ( topped) mixture is prepared, or second, the high-boiling acids (e.g. C ₂₂ or more acid) was removed from having a boiling point higher than the temperature selected, whereby cut the tail of the acid (tailed) mixture Or the removal of both lower and higher boiling acids, thereby producing a "top and tail" mixture of acids. Such fatty acid mixtures may also contain ethylenically unsaturated acids such as oleic acid. These fatty acid mixtures are accounted are esterified with methanol rise to methyl fatty acid ester mixtures, it is hydrogenated mixture of alkanol, to produce, for example, alkanols of C ₈ to C ₂₀ (often referred to as detergent alcohols), these Are suitable for the preparation of detergents without prior separation of the alkanols from one another. Such hydrogenation may be in the liquid or vapor phase (where the hydrogenation conditions are selected such that the vapor mixture in contact with the catalyst is always above its dew point, preferably at least about 5 ° C. above its dew point. Is advantageous). Examples of suitable hydrogenation catalysts may include copper-chromite and reduced copper oxide-zinc oxide hydrogenation catalysts of the type disclosed in GB-B-2116552.

Another class of carboxylic acid esters may be prepared by the process of the present invention are aliphatic and cycloaliphatic C ₄ to C ₁₈ dialkyl esters of saturated and unsaturated dicarboxylic acids.
These are alkanols and dicarboxylic acids or their anhydrides,
Or it can be prepared by reaction with a mixture of dicarboxylic acid and its anhydride. Dialkyl acrylates, dialkyl maleates, dialkyl succinates, dialkyl fumarate, dialkyl glutarates, dialkyl pimerates and dialkyl azelates are examples of such dicarboxylic esters. Other examples of such esters include dialkyl esters of tetrahydrophthalic acid. C _{1 of} such a dicarboxylic acid
To C ₁₀ alkyl esters of particular interest. Free dicarboxylic acid or anhydride (if present) or a mixture of dicarboxylic acid and anhydride can be used as the carboxylic acid component starting material for the preparation of such dialkyl esters. Alkyl esters of aromatic C ₇ to C ₂₀ monocarboxylic acids and mixtures thereof can make the process of the present invention.
Benzoic acid and 1-naphthoic acid are examples of such acids.

The alkyl esters have also the process of the present invention the aromatic C ₈ to C ₂₀ dicarboxylic acids, acid may be prepared from their anhydrides, and mixtures thereof.

It is also possible to produce polyalkyl esters of polycarboxylic acids by the process of the present invention. Such polycarboxylic acid moieties include, for example, citric acid, pyromelic dianhydride, and the like.

Carboxylic acid esters of dihydric and polyhydric alcohols can be prepared by the process of the present invention. Examples of such esters include ethylene glycol diformate, ethylene glycol diacetate, propylene glycol diformate, propylene glycol diacetate, glyceryl triacetate, hexose acetates and sorbitol, mannitol and xylitol acetate, propionate and n -butyrate. including.

In the practice of the present invention, the more volatile component of the two, the carboxylic acid component and the more volatile component of the alcohol component, will often be the alcohol component. For example, methanol will be a more volatile component in the production of the fatty acid ester mixture from the fatty acid mixture obtained by hydrolysis of triglycerides and subsequent processing, for example, in the production of detergent alcohols by ester hydrogenation. On the other hand, in the production of di- n -butyric acid esters of ethylene glycol from n -butyric acid and ethylene glycol, for example, n -butyric acid would be a more volatile component. Similarly, in producing propylene glycol diformate from propylene glycol and formic acid, the more volatile component would be the carboxylic acid component, ie, formic acid.

Esterification conditions in the column reactor are at elevated temperatures up to about 160 ° C, for example in the range of about 80 ° C to about 140 ° C, preferably about 1 ° C.
Including use in the range from 00 ° C to about 125 ° C. Such operating temperatures will be determined by such factors as the thermal stability of the esterification catalyst, the kinetics of the esterification reaction and the vapor temperature of the vapor component fed to the base of the column reactor at the inlet pressure. Typical operating pressures at the column reactor steam inlet range from about 0.1 to about 25 bar. about
From 0.1 hr ^-1 to about 10 hr ^-1, and typically from about 0.2 hr ^-1 to about
Liquid hourly space velocities through the column reactor ranging up to 2 hr ^-1 can be used.

The alcohol component or carboxylic acid component or a mixture thereof can be fed to the top of the column reactor in liquid form, in a solution in the recycled ester product, or in an inert solvent or a solution in a diluent therefor. . In some cases, it may be desirable to react the alcohol component and the carboxylic acid component prior to introduction into the column reactor. Such a pre-reaction can be used, for example, when the reaction between the two components can be initiated in the absence of an added catalyst. An acid anhydride such as maleic anhydride or phthalic anhydride and an alkanol (eg, methanol, ethanol or
The reaction with an alcohol component such as ( n -butanol) is an example of such a reaction, and under mild conditions, for example at 60 ° C. and 5 bar, the formation of the corresponding monoester without the need for any additional catalyst is described by the formula Occurs: Wherein R ⁵ is methyl, ethyl or n - alkyl radical such as butyl. This monoester is still a monocarboxylic acid. In addition to this some formation of diesters will occur: The resulting reaction mixture may include a mixture of monoester, diester, water and alkanol. If necessary, more alkanols can be added to the mixture before introduction into the column reactor for conversion of the monoester to the diester.

In other cases, even when a monocarboxylic acid ester is a product of interest, balancing the alcohol component and the carboxylic acid component in the presence of an acidic ion exchange resin containing -SO ₃ H and / or -COOH groups And then the resulting equilibrium mixture can be introduced into a column reactor.

In the process of the present invention, the vapor mixture exits the column reactor as an overhead product. Scrubbing such a vapor mixture in liquid form with a more volatile component (usually an alcohol component) so that the carboxylate product and other components (usually the carboxylic acid component) are washed back into the column reactor. Equipment can be provided. This overhead product from the column reactor is condensed, treated in a known manner to separate its constituents, the recovered esterified water is eliminated and the more volatile components (usually alcohol components) Will be recycled for reuse as dry as practicable within the economic constraints. The lower the water content of the steam fed to the lowest of the esterification trays, the more the esterification equilibrium reaction towards 100% conversion to ester proceeds, and the ester-containing product recovered from the bottom of the column reactor Will have lower residual acidity. However, on the one hand, the costs of providing substantially dry alkanols, e.g. for vaporization in a column reactor, and grade the ester product to the required quality if less dry alkanols are used A balance must often be struck between the cost of installing and operating additional downstream processing equipment that would be required to increase the cost. This will change from alkanol to alkanol and will depend on the interaction between water and alkanol (eg, azeotropic formation) and its effect on alkanol / water separation. Preferably, when using alkanol vapor flowing upward in the column reactor, the water content of the alkanol vapor supplied to the reactor is less than about 5 mol%, and even more preferably less than about 1 mol%.

The column reactor has a plurality of esterification trays. 2
While it is sufficient if there are also single or three trays, it will generally be necessary to provide at least about 5 to about 20 or more esterification trays in the column reactor. Generally, each esterification tray is designed to have a residence time for the liquid on each tray of from about 1 minute to about 120 minutes, preferably from about 5 minutes to about 60 minutes.

Solid esterification catalysts particulate -SO ₃ H and / or -COOH
It can be a particulate ion exchange resin containing groups. This form of macroreticular resin is preferred. Examples of suitable resins include the trademark "Am
berlyst "," Dowex "," Dow "and" Purolite ". Amberlyst 13, Amberlyst 66, Dow C351 and
Like the Purolite C150.

Different solid esterification catalysts can be used on separate trays of the column reactor. Further different concentrations of solid esterification catalyst may be used on separate trays.

The charge of solid fine or granular esterification catalyst on each tray is generally at least 0.2% w / v resin concentration on that tray as dry resin, for example 2% w / v to 20% It is sufficient to provide a catalyst: liquid ratio corresponding to a resin concentration in the range of w / v, preferably 5% w / v to 10% w / v. Sufficient catalyst should be used on the tray to allow equilibrium or near-equilibrium conditions to be established within the selected residence time at the operating conditions. On the other hand, large amounts of catalyst should not be used on each tray so that it is difficult to keep the catalyst suspended in the liquid due to the agitation created by the upflowing steam entering the tray from below. For typical resin concentrations, from about 2% v / v to about 20% v / v, preferably 5% v / v to 10% v / v.
Resin concentrations ranging up to v can be used.

The size of the catalyst particles should be large enough to allow the catalyst to be held by a screen or similar device on each tray. However, using too large a catalyst particle size is not possible because the larger the size of the catalyst particles, the more difficult it is to keep in suspension and the lower the geometric surface area per gram. Not a good idea. Suitable catalyst particle sizes range from about 0.1 mm to about 5 mm.

One or more wash trays are provided above the esterification trays to prevent product, solvent and / or reactant losses from the column reactor.

In a column reactor, the vapor riser means associated with each esterification tray has a sparger, which in operation is below the surface of the mixture of liquid and solid esterification catalyst on that tray; The vapor bubbles emerging therefrom are then positioned to stir the mixture of liquid and solid esterification catalyst. The sparger may be a ring sparger. At least one baffle means is provided near the sparger to increase its mixing action. For small scale operations, a sparger below a cylindrical baffle on the axis of the column reactor can be used.

In one embodiment, the sparger is a ring sparger, and the inner and outer annular baffle means are located near the sparger to define an ascending zone in the region of the ascending steam bubble and within the ascending zone. And an outwardly adjacent downflow zone.

It is important to avoid stagnation zones where solid esterification catalysts settle. This can lead to excessive formation of by-products or the occurrence of hot spots. Although a mechanical stirrer can be provided on each tray to keep the catalyst particles suspended in the liquid, this does increase the complexity of the reactor somewhat. However, the proper design of the spargers and trays can provide sufficient agitation as the ascending vapor passes through the liquid on the trays, ensuring that the catalyst is kept in suspension. To this end, at least a portion of one or more (and preferably all) of the floors in the esterification tray is caused by ascending steam as found under the sparger. It is convenient if it is inclined towards the zone where the turbulence is present. The slope angle is preferably selected to be equal to or greater than the angle of repose of the solid particulate esterification catalyst below the liquid in the esterification tray. The use of such a slope ensures that all of the catalyst is in dynamic contact with the liquid during operation and that no stagnation zone of the catalyst is formed. Such stagnation zones are undesirable because they allow for unwanted side reactions or, in some cases, even thermal runaway.

In a preferred apparatus, one or more (and preferably all) the vapor riser means of the esterification tray are provided with liquid back-suction prevention means.

Screen means may be provided on at least one esterification tray to prevent losses from the esterification tray of the solid esterification catalyst via the combined downcomer means. In this way, downflow of solid catalyst from one esterification tray to the next lower one can be substantially prevented.

During operation of the column reactor, means may be provided for removing resin from or adding resin to one or more trays. For example, a conduit having an open end bent downward extends into the interior of each tray, with its open low end located at a low point in the tray. By this means, a slurry of catalyst and liquid can be removed from the tray in a controlled manner, intermittently or continuously, as desired, or more catalyst can be removed to the tray in the form of a slurry,
It can be introduced as desired. The catalyst removed from a given tray can be reintroduced into the column reactor, either in the same tray or to a lower or higher one, possibly after being given a regeneration treatment.

In order that the invention be clearly understood and can be readily practiced, three preferred types of plants for the continuous production of esters and corresponding preferred processes for use in connection therewith are set forth below. It will be described with reference to the accompanying drawings only. In these figures: FIG. 1 is a flow diagram of a plant for the production of a methyl ester of a fatty acid constructed according to the teachings of the present invention; FIG. 2 is a flow diagram of a plant for the production of a carboxylic acid ester; Have a boiling point significantly higher than that of the alcohol from which the alcohol moiety is withdrawn, than of water, or of any alcohol / water azeotrope formed; FIGS. Details of parts of the design are shown; and FIG. 6 is a flow diagram of another plant.

Those skilled in the art will recognize that the drawings are schematic and refer to such as reflux drums, pumps, vacuum pumps, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks, etc. It will be appreciated that such additional items of equipment are required in a real plant. The installation of such ancillary equipment does not form part of the present invention, but rather is through the practice of conventional chemical engineering.

Referring to FIG. 1 of the drawings, methanol is supplied to the plant in line 1 and mixed with recycled methanol in line 2 to form a methanol feed to the plant in line 3. The fatty acid mixture, for example obtained by hydrolysis of a naturally occurring triglyceride, for example coconut oil, followed by "topping and tailing", is charged in line 4 and mixed with the methanol charge from line 3 before the heat exchanger. 5 where the temperature is raised to 110 ° C. The heated acid / methanol mixture flows in line 6 to the main esterification reactor 7, which comprises a charge 8 of an ion exchange resin containing sulfonic and / or carboxylic acid groups, such as Amberlyst 13. (“Ambe
The term "rlyst" is a trademark.) The pressure in the reactor 7 is 5 bar.

In the reactor 7, a portion of the acid mixture is esterified by reaction with methanol to yield a corresponding mixture of methyl fatty acid esters. From the reactor 7, a mixture of methyl ester, unreacted fatty acids, water produced by the esterification and unreacted methanol exits via line 9. This mixture passes through a pressure drop valve 10 to a vapor / liquid separator 11. The vapor phase consisting of methanol and water is 1.3 bar at line 12
And 13 to the top of the esterification reactor.
Reactor 14 comprises a number of esterification trays 15; two possible forms of esterification trays 15 are illustrated in FIGS. 3 and 4 and will be described in detail below. In the plant of FIG. 1, there are six trays 15; however, a larger or smaller number of such trays (eg, 3 to 5 or 7)
From 20 to any number) can be provided according to the nature of the fatty acid and the reaction conditions chosen.

The liquid phase from the vapor / liquid separator 11 is charged to a heat exchanger 19 by a line 16, a pump 17 and a line 18, in which it is heated by steam to a temperature of up to 150 ° C, for example 120 ° C,
The line 20 is then charged into the reactor 14 at a point below the entry point of the line 13.

In the reactor 14, the unreacted fatty acids flowing down in the mixture in line 20 are transferred from each esterification tray 15 to the next lower tray 15 with methanol and esterified water, i.e., water produced as a result of the esterification reaction. And passes downward against the upward flow of the vapor consisting of Dry methanol vapor is supplied to reactor 14 on line 21. Each esterification tray 15 holds a charge of an acidic ion exchange resin, such as a resin containing sulfonic acid groups. Amberlyst 13 is a suitable resin. (Amberlyst is a trademark). Downward passing column 1
In 4, unreacted free acid encounters drier methanol vapor on each tray 15 in turn. By designing each tray 15 to provide appropriate liquid retention, each tray 15
It is possible to regulate the residence time above. By selecting an appropriate number of trays 15, additional reactor 14 is left in the liquor that essentially passes any free fatty acids down from bottom tray 15 into a sump 22 below the reactor. It is possible to design so as not to. The methyl ester product (ie, a mixture of methanol and methyl ester derived from the mixed fatty acids provided in line 4)
It is removed from the sump 22 at 23 and pumped via line 25 by a pump 24 for further processing or to a product purification facility or to storage.

A mixture of methanol vapor and the water released from the esterification reaction is recovered overhead from reactor 14 in line 26. Liquid methanol is supplied at line 27 to the top of the reactor 14 above the junction of line 13 and provides liquid methanol on a wash tray 28.

The steam in line 26 is charged to a methanol / water separation column 29, which operates at 1.3 bar and a head temperature of 70 ° C. Dry methanol vapor is collected overhead in line 30 and condensed in condenser 31. The resulting condensate is collected on drum 32, which is vented as indicated at 33. The dimethyl ether produced as a by-product is withdrawn in line 33. Methanol, which may be lost with dimethyl ether, goes to line 31
Can be recovered by providing a quench condenser (not shown). The condensed methanol goes to column 29 and is drummed
It is recycled as a reflux stream from 32 to line 34 by pump 35 and lines 36 and 37. The rest is a line
Pumped back for reuse at 38.

The bottom sump product from column 29 consists essentially of water. This is retrieved at line 39. Part is column 29
To line 40, steam heated reboiler 41 and line 42; the remainder goes to line 43 for effluent treatment.

Some of the dry methanol in line 38 passes through vaporizer 44 to provide line 21 with a dry methanol vapor stream.
The remainder flows through line 45 to provide a recycle stream to lines 2 and 27.

In a variant of the plant of FIG. 1, the reactor 7 and the vapor / liquid separator 11 are omitted, and the mixture of fatty acids and methanol is charged to the line 13 by the line 46.

In another variant of the plant of FIG. 1, lines 1 to 3 and items 6 to 12 and 16 to 20 are omitted. Thus, a liquid fatty acid or mixture of fatty acids is the only liquid charge to the reactor 14 and is supplied by lines 4, 46 and 13. Complementary methanol to the plant may be supplied to reflux drum 32 via line 47.

FIG. 2 shows other forms suitable for the production of mono-, di- and polycarboxylic esters having a boiling point significantly higher than the boiling point of the alcohol used and of any water / alcohol azeotrope that can be produced. 1 illustrates a plant.

In the plant of FIG. 2, the same reference numbers are used to indicate similar parts as those present in the plant of FIG. 1, except that line 1 is not for the supply of methanol, but for ethanol or 10 It is used for the supply of higher alcohols containing up to carbon atoms. Line 25
The products therein are therefore ethyl or higher esters of mono-, di- or polycarboxylic acids. Reference numeral 48 indicates any suitable alkanol / water separation plant.

Similar modifications to the plant of FIG. 2 can be made to those described above. That is, items 1 to 3, 6 to 12 and 16
The omission of through 20 allows the supply of the liquid fatty acid or fatty acid mixture as the only liquid charge to the reactor 14.

FIG. 3 shows the tray of the reactor 14 of the plant of FIGS.
One form of the 15 structures is illustrated. Horizontal diaphragm or partition 50
Extends into the wall 51 of the reactor 14 and completely closes off the cross section of the reactor 14 except for a downcomer 52 and a vapor riser 53 for the liquid. The bulkhead 50 is an axial frustoconical section 54 surrounding the steam riser 53 and an annular sloped section adjacent the wall 51
Has 55. Tray 15 can thus hold a volume of liquid, its surface is indicated by 56, and its volume is
It is determined by the height of the overflow level of the downcomer 52 above 50. Each tray acidic ion exchange resin support comprising also a quantity of such -SO ₃ H group of Amberlyst 13, the particles are indicated by the schematically 57. Such ion exchange particles are held suspended in the liquid on the tray 15 as a result of the agitation caused by the rising vapor, as described below. In order to prevent the ion exchange resin particles 57 from escaping with the liquid flowing down the overflow pipe 52,
At the top of the downcomer 52, a screen 58 is provided. The slope of the frusto-conical portion 54 and the ramp 55 is equal to or greater than the angle of repose of the Amberlyst 13 or other solid particulate esterification catalyst beneath the liquid on the esterification tray 15.

A steam riser 53 is used to transfer the rising steam into a circular sparger 59.
Which surrounds the frustoconical portion 54 by a spider tube 60. Suckback of the liquid riser tube 53 is prevented by the anti-suckback valve 61.

An annular draft side plate or baffles 62 and 63
Within the upper liquid body, one located inside the circular sparger 59 and one located outside, facilitates agitation of the liquid / resin suspension by the rising vapor. The vertical length of the side plates 62 and 63 is not critical, but should generally be between 1/3 and 3/4 of the vertical height between the diaphragm 50 and the liquid surface 56. Side plate 62 and
63 is preferably located in a symmetric or near-symmetric vertical position. In the annular zone between the side plates 62 and 63, the liquid flow is generally upward, while the inside of the side plates 62 and the side plates 63
Outside of, the general direction of liquid flow is downward. Preferably, the area of the annular zone between the side plates 62 and 63 is approximately equal to the sum of the area inside the side plates 62 and outside the side plates 63.

Reference numeral 64 indicates a downcomer 64 from the next tray above that shown in FIG. The liquid level in the downcomer 64
Indicated at 65, the height H of this liquid level above the liquid level 56 on the tray 15 is the liquid level on the tray feeding the downcomer 64 (i.e. the tray above the illustrated tray 15), plus that tray (i.e. It is determined by the pressure drop and the friction pressure drop through the sparger 59 on the tray 15 shown).

In the operation of the reactor 14, the mono-, di- or polycarboxylic acid or mixture of acids is passed downward, generally in liquid form, countercurrent to the rising alcohol vapor stream. Each tray 15 acts as an esterification zone containing a respective amount of esterification catalyst, which catalyzes the esterification reaction and the release of esterification water. Under prevailing countercurrent conditions in the reactor 14, such esterified water vaporizes and is carried upward with the alcohol vapor flowing upward through the reactor 14.
The liquid passes downward from one tray 15 to the next lower tray 15, the free acid concentration in the liquid on each tray 15 being lower than the corresponding acid concentration in the liquid on the next higher tray 15. In addition, as the liquid passes down through the reactor 14,
Dryer and drier alcohol on each tray is encountered. In this way, the equilibrium of the esterification reaction is further pushed towards ester formation, and the reverse hydrolysis reaction is effectively suppressed. This is because the water concentration in the liquid on the tray 15 decreases from tray to tray in the downward direction.

By choosing an appropriate number of trays 15 in column 14,
And by designing each tray to provide sufficient liquid retention to provide the required residence time on each tray, the product in line 25 can be connected to reactor 14 as its major component. Can be designed to contain no more than about 1 mole% of carboxylic acids together with the fatty acid esters and alcohols. By providing a suitable upward flow velocity to the alcohol vapor, the agitation caused by the vapor bubbles 66 emerging from the circular sparger 59 is combined with the liquid circulation induced by the presence of the draft side plates 62 and 63. Is sufficient to keep the acidic ion exchange resin particles sufficiently suspended to allow the esterification to proceed successfully. The surfaces of compartments 54 and 55 slope toward the zone below sparger 59 to ensure that there are no stagnation zones where significant amounts of resin can settle out of the suspension. (Although FIG. 3 shows only resin particles 57 suspended in the zone between draft side plates 62 and 63,
They will in fact also be suspended in the liquid phase outside this zone. 3.) If necessary, the volume of the rising vapor can be boosted by an inert gas or other vaporizable inert material, conveniently a by-product of the process. For example, ethers are often found in by-products, as acidic catalysts can promote the formation of ethers from the alcohols used. Thus, dimethyl ether is a potential by-product if methanol is used as the alcohol, while diethyl ether can be found in reactor 14 if ethanol is the alcohol used; If necessary, it can be used to boost the steam flow to provide additional agitation on tray 15 or to provide additional steam to carry away the esterification water.

FIG. 4 illustrates another design of an esterification tray 15 suitable for use in a relatively small scale reactor 14. In this case, the frustoconical partition or septum 70 extends into the wall 71 of the reactor 14 and the cross section of the reactor 14 is completely closed except for the downcomer 72 and the vapor riser 73 for the liquid. I do. The inclination of the truncated conical diaphragm 70 is tray 15
It is equal to or greater than the angle of repose of the solid particulate catalyst below the overlying liquid. The steam riser 73 includes an axial sparger 74, which is provided with a bubble cap 75 and fitted with a check valve 76. Optionally, bubble cap 75 may be surrounded by a mesh screen (not shown) to prevent ingress of catalyst particles that would interfere with operation of valve 76. A cylindrical baffle 77 symmetrically surrounds the sparger 74 and is located below the liquid level 78, the height of the liquid level being determined by the height of the upper end of the downcomer 72. A screen 79 is mounted on top of the downcomer 72 to hold a solid esterification catalyst, such as Amberlyst 13, on the tray 15. Reference number 80 is the next higher esterification tray
Indicate the downcomer from 15 (not shown). In a manner similar to that described with respect to FIG. 3, the steam valve 81 stirs the liquid on the tray 15 to keep the catalyst particles in suspension. Baffle
77 defines an upflow zone inside the baffle 77
77 A downflow zone is defined outside. Preferably, the areas of the two zones are substantially equal. This design ensures, wherever possible, that no stagnation zones are formed in which the catalyst particles can settle.

If desired, the feed line 20 or 13 in the plant of FIGS. 1 and 2 is arranged to discharge onto a tray that does not hold a certain amount of ion exchange resin, similar to the tray 15 of FIG. 3 or 4. Can be done. One or more alkanol wash trays are provided above the connection of feed line 20 or 13 so that the vapor is washed with a small amount of liquid alcohol before exiting reactor 14 on line 26 to remove any acid or ester therein. Can be limited to trace.

FIG. 5 illustrates another design of an esterification tray suitable for use in a laboratory scale reactor 14 or a commercial scale reactor 14. This is the wall 251 of reactor 14
It has a generally frusto-conical septum or diaphragm 250 extending into it. The inclination of the upper surface of the diaphragm 250 is larger than the angle of repose of the solid particulate catalyst. A cap 253 is attached to the steam riser 252, which has an attached mesh skirt 254. A mesh cap 256 and a seal bucket 257 are attached to the downcomer pipe 255. The upper end of the downcomer 255 is a tray
15 to provide a suitable holding volume for the liquid above, while mesh skirt 254 and mesh cap 256
Holds the charge of resin particles on the diaphragm 250. The methanol vapor flows up riser 252 as indicated by arrow 257, flows through the space between riser 252 and cap 253 as indicated by arrow 258, and through skirt 254 as indicated by arrow 259. The stream carries with it the water vapor resulting from the esterified water formed in the lower tray (s).

The plant of FIG. 6 is generally similar to that of FIG.
Like reference numerals have been used to indicate like parts in both figures. The charge in line 4 is generally an unsaturated fatty acid such as oleic acid.

In the plant of FIG. 6, line 2 is omitted, so there is no methanol recycle to be mixed with the charged methanol in line 1. There, all methanol in line 45 is supplied to the cleaning tray 28.

The number of theoretical plates in column 14 does not necessarily correspond to the number of trays 15 mounted in column 14, and the number of such theoretical plates may vary for different columns depending on the different charge acids supplied to line 4 for a particular column. Since it can vary accordingly, the acid content of the methyl ester product in line 23 can vary if the nature of the charged acid in line 4 is varied.

As mentioned, the by-product of ester formation in the column is often a dialkyl ether. It has been found that the amount of such dialkyl ether by-products depends on the operating temperature of the reactor 14. Thus, by minimizing the operating temperature of the column reactor, by-product ether production can be minimized. The corollary, however, is that less conversion of the acid to the ester is obtained at lower operating temperatures. In this case, the conversion to the ester can be optimized by mixing the ester-containing product, which is likely to have an acidic balance of about 97 mol% to about 99 mol% of the ester. The resulting mixture, further comprising an alkanol (eg, methanol) and comprising, for example, a 2: 1 to 4: 1, eg, 3: 1 alkanol: ester molar mixture, is treated with a fixed bed of a solid esterification catalyst such as Amberlyst 13. Through a finished reactor having a lower temperature than the column reactor. In this way, very high overall ester conversions can be achieved. Such a plant variant is illustrated in FIG.

In the plant of FIG. 6, six esterification trays
And the methyl ester product in line 23 still contains a small amount of oleic acid. Generally, the molar ratio of methyl oleate: oleic acid is in the region of 97: 3. This mixture is mixed with additional methanol supplied from line 301, resulting in methanol: methyl oleate: oleic acid.
A mixture having a molar ratio of 3: 0.97: 0.03 is formed. This mixture is fed in line 302 at a temperature of 60 ° C. and a liquid hourly space velocity of ¹ hr ⁻¹ to another esterification reactor 303 containing a fixed bed 304 of an acidic ion exchange resin such as Amberlyst 13. The resulting mixture flows through line 305 to another distillation column 306. The methanol vapor passes overhead via line 307 and to column 29 via line 26. The liquid methanol forms a reflux stream and the line
This stream of 301 is pumped from condensate drum 32 by pump 35 through line 308. The reflux flow flows along line 309 to column 306. Line 3 from column 306
The bottom product in 10 consists essentially of pure methyl oleate (at least 99.5 mole% pure). Part of it is recycled to column 306 via line 311 via column reboiler 312 and line 313, while the remainder is sent to storage at line 314 or to further processing.

The plants of FIGS. 1 and 2 and the trays illustrated in FIGS. 3 and 4 have been described in relation to the descending stream of acid-containing liquid and the ascending vapor alcohol stream. If the acid used is more volatile than the alcohol component, then the direction of flow of the acid and alcohol component can be reversed, in which case the alcohol is in the liquid phase and the next from one tray 15 Reactor into tray 15 below
It flows downward through 14, while the acid vapor passes upwards countercurrent thereto.

 The present invention is further described in the following examples.

Example 1 A laboratory scale column reactor with 10 trays stacked on top of each other and made of glass QVF parts with an inner diameter of 76.2 mm was used. Each tray had the shape shown in FIG. The column reactor was covered and wrapped with an outer electric heating tape. Each tray had its own temperature control system. The top tray contained no resin and served as a liquid wash tray to limit acid charge or ester product loss. The second tray from the top also contained no resin and was supplied with an acid charge. The remaining eight trays each held a quantity of Amberlyst 16 ion exchange resin, which was sieved to remove beads having a particle size of 355 μm or less, then thoroughly washed with methanol and
Dried to constant weight at ° C. Skirt 254 and cap 256
The mesh size of stainless steel mesh is 300
μm. The dry methanol was vaporized by passing through a coil immersed in an oil bath at 150 ° C., and the resulting vapor was charged under the bottom tray at the bottom of the column reactor. Each tray held 240 ml of liquid. The loading of resin on each tray corresponds to 14% by weight calculated as dry resin based on the loading of liquid on each tray. The overhead vapor from the column reactor, which consisted of unreacted methanol, water formed during the esterification and a small amount of by-product dimethyl ether, was condensed. A head overflow device is used to control the rate of product ester removal from the column reactor.

To start, the column reactor was charged with resin and methyl laurate. When the methanol stream and the temperatures of the various trays were stable, 50 mol% of methyl laurate, 40
A charge of 10% lauric acid and 10% myristic acid was fed to the column. The charge mixture was similar to the mixture in line 20 of FIG. 1 when the plant was fed in line 4 with a mixture of lauric and myristic acid. Level of C ₁₄ esters of the bottom product from the column reactor was monitored until an equilibrium level is reached. The liquid on each tray was analyzed. The results are summarized in Table I below; trays are numbered from 1 to 10 and tray No. 1
Is the top tray, and tray No. 10 is the bottom tray.

In Table I and the following tables, "ND" means "not determined", while "DME" means "dimethyl ether" and "DME formed" is expressed as weight percent acid charge.

Example 2 The same column reactor used in Example 1 was charged with a mixture of natural linear fatty acids of the following composition: component weight% C ₈ acid 5.10 C ₁₀ acid 4.62 C ₁₂ acid 40.64 C ₁₄ acid 14.12 C ₁₆ acid 9.57 C ₁₈ acid 25.01 Unknown 0.77 H ₂ O 0.17 The results are summarized in Table II.

Example 3 The procedure of Example 2 was repeated using an acid: ester molar ratio of 51.6: 48.4. Such a mixture is shown in line 20 in FIG.
Corresponds to the general charge mixture. The acid used was
65 wt% C ₁₂ acid, was a mixture of natural straight chain fatty acids consisting of 25% C ₁₄ acid and 10 wt% C ₁₆ acid. The result is III below
Shown in the table. In this example, the amount of resin used on each tray on a dry basis was equivalent to 10% by weight based on the retained liquid for each of trays Nos. 3-7, and For 10 it was equivalent to 5% by weight on the same basis.

Example 4 The column reactor of Example 1 was replaced with monoethyl maleate (ME
M) was used to investigate the formation of diethyl maleate (DEM) by esterification with ethanol. The amount of resin charged in the tray was the same as in Example 3. The acid charge to tray No. 2 had the following composition in mole%: water 25.9; EtO
H20.3; DEM10.4; diethyl fumarate (EEF) <0.1; MEM3
9.4; Monoethyl fumarate (MEF) 0.1; Maleic acid (MA
C); fumaric acid (FAC) <0.1; diethyl ethoxysuccinate (EDES) <0.1. Examples 1 to 3 of wet ethanol
The dry methanol used was replaced; it had the following composition in mole%: EtOH842; water 15.8. The residence time in the column reactor was about 2.7 hours. Preparation speed is 680g /
hr, acid charge and 390 g / hr ethanol. The result is I
Shown in Table V.

In this example, diethyl ether was a by-product; the amount of diethyl ether formed corresponded to about 16 g / kg of monoethyl maleate.

Example 5 The procedure of Example 4 was repeated, but with a residence time in the reactor of about 2.1 hours, using the same feed mixture. The acid feed rate is 840 g / hr, and the ethanol feed rate is 475 g / hr.
hr. The results are summarized in Table V.

In this example, diethyl ether was a by-product; the amount of diethyl ether formed corresponded to about 11 g per kg of monoethyl maleate.

Examples 4 and 5 show the benefits of using a column reactor, which uses an alcohol: acid molar ratio of about 2: 1 and
It allows a mole% conversion of 84.0 and 81.7, respectively, to be achieved. Using a fixed bed reactor, the maximum mole percent conversion is about
Could be shown to be 72%, then about 5: 1
It may be necessary to use an alcohol: acid molar ratio of
Similarly, when using a continuously stirred tank reactor,
A conversion of 80% or more can likewise only be achieved when a much higher alcohol: acid molar ratio, for example about 5: 1, is used instead of about 2: 1.

Example 6 Using the column reactor of Example 1, monomethyl maleate (MMM) was reacted with dry methanol (MeOH) under the conditions indicated in Table VI, which also shows the results obtained. ing. The mole% conversion figures were obtained by titration.

Example 7 Following the general procedure of Example 6, a product was produced containing substantially pure dimethyl maleate (DMM) but still a small amount of monomethyl maleate (MMM) in addition to the traces of water. This product was mixed with dry methanol and passed co-current through a finishing reactor containing Amberlyst 16 similar to reactor 304 in FIG. The result obtained is Section VII
It is summarized in the table.

Example 8 The following esterification reaction between the specified acid and the corresponding alcohol component using the column reactor of Example 1 is carried out with equally good results, or in each case more volatile Are supplied in vapor form to the bottom of the reactor and the more non-volatile components are supplied in liquid form to the second tray of the reactor: (a) from succinic acid and n -propanol Di-succinic acid
n - to propyl; from (d) acid and phenol; (b) maleic acid mono - to butyl n - butyl and the n - maleic acid di butanol - - n; (c) from terephthalic pentanol acid and methanol to terephthalic acid dimethyl (E) glutaric acid and ethanol to diethyl glutarate; (f) acid and ethanol to diethyl acid; (g) benzoic acid and ethanol to ethyl benzoate; (h) 1-naphthoic acid and methanol To methyl 1-naphthoate; (i) acetic acid and ethylene glycol to ethylene glycol diacetate; (j) stearic acid and methanol to methyl stearate; (k) palmitic acid and ethanol to ethyl palmitate; ) Arachidic acid and arachidic acid from ethanol To chill; (m) butyric acid and the n - nonanol butyric acid n - to nonyl; (n) citric acid and ethanol to citrate ethyl;
And (o) formic acid and propylene glycol to propylene glycol diformate; (p) oleic acid and isopropanol to isopropyl oleate; (q) ricinoleic acid and methanol to methyl ricinoleate; and (r) isostearic acid and methanol. To methyl isostearate.

Continued on the front page (72) Inventor Wood, Mikle, Anthony Cleveland Thies 7.0 Cuees, Middlesbrough, Nunthorpe Watchgate 2 (72) Inventor McKinley, Donald Hugh Hertfordshire, United Kingdom Dove Rudy 7.8 Eidsey, Ladlet, Goodyer Avenue 55 (58) Fields studied (Int. Cl. ⁶ , DB name) C07C 69/02-69/22 C07C 67/08 B01J 8/22 WPI / L (QUESTEL) EPAT (QUESTEL)

Claims (19)

(57) [Claims] 1. A carboxylic acid component selected from mono-, di- and polycarboxylic acids, anhydrides and mixtures thereof, and mono-, di- and polyhydric alcohols, phenols and mixtures thereof. Continuous process for the production of a carboxylic acid ester by reaction with a selected alcohol component, wherein the carboxylic acid component and the alcohol component are maintained under esterification conditions and have fine particles having sulfonic acid groups, carboxylic acid groups or both. Column reactor with a plurality of esterification trays arranged one above the other in a process in which the esterification zone is passed countercurrently through an esterification zone containing a solid esterification catalyst selected from the state of ion exchange resin Each tray has a predetermined liquid volume and a certain amount of solid esterification catalyst held thereon, and each ester Having a liquid downcomer means associated with the tray, allowing the liquid phase to pass down through the column reactor from its esterification tray but retaining the solid esterification catalyst thereon, and in combination with each esterification tray Steam riser means to allow the steam to enter the esterification tray from below, to stir the mixture of liquid and solid esterification catalyst on the tray, and to provide a more volatile mixture of carboxylic and alcohol components. The less volatile component is supplied in the liquid phase to the top one of the plurality of esterification trays, while the more volatile component of the carboxylic acid component and the alcohol component is the most volatile of the plurality of esterification trays. It is supplied in vapor form under the lower tray, and the vapor of the more volatile components and the water of esterification are recovered from the top of the column reactor and Le a continuous process for the preparation of carboxylic acid esters, characterized in that it is recovered from the bottom of the column reactor. 2. The process according to claim 1, wherein the more volatile component is an alcohol component and the less volatile component is a carboxylic acid component. 3. The process according to claim 1, wherein the alcohol component is an alkanol containing 1 to about 10 carbon atoms. 4. The process according to claim 3, wherein the alkanol is methanol. 5. The process according to claim 3, wherein the water content of the alkanol vapor supplied to the column reactor is less than about 5 mol%. 6. A process according to claim 1, wherein the carboxylic acid component is an aliphatic monocarboxylic acid or a mixture thereof. 7. The process according to claim 6, wherein the carboxylic acid component is a mixture of fatty acids. 8. The method according to claim 1, wherein the carboxylic acid component is maleic acid, fumaric acid, maleic anhydride, monoalkyl maleate, monoalkyl fumarate, or a mixture of two or more thereof. Process by any one. 9. The method according to claim 1, wherein the column reactor is operated at a temperature of about 80 ° C. to about 140 ° C. and a pressure of about 1 bar to about 25 bar. process. 10. The method according to claim 1, wherein the carboxylic acid ester recovered from the lower part of the column reactor is mixed with an additional alcohol component and passed through a fixed bed of a solid esterification catalyst. One-by-one process. 11. A carboxylic acid component selected from mono-, di- and polycarboxylic acids, anhydrides and mixtures thereof, and mono-, di- and polyhydric alcohols, phenols and mixtures thereof. An apparatus used for the production of carboxylic esters by reaction with an alcohol component, comprising a column reactor with a plurality of esterification trays arranged one above the other, each tray being defined in advance. And a liquid downcomer means associated with each esterification tray, and the liquid phase is converted to a column reactor by esterification. Passed down from the tray but adapted to retain the solid esterification catalyst thereon, having a vapor riser means in combination with each esterification tray, wherein the steam is The mixture enters the tray from below, and the mixture of the liquid and solid esterification catalyst on the tray is agitated. Means for feeding to the top of the column reactor above the top tray in the esterification tray and the more volatile components of the carboxylic acid and alcohol components below the bottom esterification tray. Means for feeding the lower part of the column reactor in vapor form, means for recovering the carboxylic acid ester from below the lower column reactor below the lowermost esterification tray, An apparatus for producing a carboxylic acid ester, comprising means for recovering a vapor stream comprising the more volatile components and the water of esterification above a top esterification tray. 12. The steam riser means has a sparger which, in operation, is below the surface of the mixture of liquid and solid esterification catalyst, and vapor bubbles emanating therefrom are mixed with the liquid and catalyst. Is positioned to stir the mixture of
Device according to claim 11. 13. The apparatus according to claim 12, wherein the sparger is a ring sparger. 14. Apparatus according to claim 12, wherein at least one baffle means is provided near the sparger to increase its mixing action. 15. An inner and outer annular baffle means is located near the sparger to define an upflow zone in the region of the rising steam bubble and to define a downflow zone adjacent to the inside and outside of the upflow zone. Apparatus according to claim 14 as defined. 16. The apparatus according to claim 12, wherein at least one floor of the esterification tray is inclined toward a zone below the sparger. 17. The steam riser means of at least one of the esterification trays is provided with back-suction prevention means.
An apparatus according to any one of claims 16 to 16. 18. A method according to claim 12, wherein screen means are provided on at least one esterification tray to prevent loss of catalyst from the esterification tray via the combined downcomer means. Device by one or the other. 19. Another reactor comprising a fixed bed of solid esterification catalyst connected downstream from a column reactor;
Means for mixing the additional carboxylic acid component with the carboxylic ester component recovered from the lower portion of the column reactor prior to entry into another reactor.
An apparatus according to any one of the preceding claims.